Because of two technologies

1) CG-NAT

2) IPv6

You literally can not have one unique IPv4 address per mobile phone.

So? Is your argument that it’s so cheap that everyone should get an IP? That would be mathematically impossible.

If more people wanted an IP, the price would just rise. The same percentage of people (less than 1/3) would have one. They would just pay more.

It’s like buying land in a city like SF. Demand can change the price, but the supply remains the same.

The argument is that migrating to IPv6 isn't worth anyone's time. (Except for maybe CG-NAT operators.)

The number of people behind CGNAT is huge and rising. It's collectively worth it. And really not that much effort. (If your internal business network is sufficiently entrenched you don't have to change it.)